Ukraine crisis: Battle rages for Debaltseve despite truce
Rebels say they have taken most of Debaltseve, a transport hub, but the government says it is still holding its positions.
International observers tasked with monitoring the ceasefire have been unable to enter the town.
Meanwhile, Ukraine accused separatists of breaching the ceasefire and said hopes for peace were being destroyed.
At a news conference, presidential spokesman Valery Chaly called on participants in the Minsk talks, members of the EU and Nato to protest strongly against the actions of the rebels.
French Foreign Minister Laurent Fabius said "fundamental" parts of the ceasefire were not being respected, referring to the Debaltseve fighting and withdrawal of heavy weapons.
Earlier, both sides failed to begin the withdrawal, despite a Monday deadline agreed in the truce.
The two sides were given until two days after the latest ceasefire came into effect to start the pullout.A spokesman for the self-proclaimed Donetsk People's Republic (DPR) told Russian news agency Interfax that the police station in Debaltseve had been taken as well as the railway station.
He said most of the city was under the control of the separatists and that a mopping-up operation was continuing.Another DPR spokesman said government forces had stepped up their bombardment and were heading towards the rebel-held town of Lohvynove in an attempt to break through to Debaltseve.
Eduard Basurin also said the rebels intended to withdraw heavy weapons from "quiet sectors" of the front line, though he gave no time-frame.
The rebels said that up to 300 Ukrainian troops in Debaltseve had surrendered, and Russian TV showed footage of what it said were 72 captured soldiers.
The Ukrainian government said a group had been taken prisoner after an ambush but denied large-scale surrenders.
The Ukrainian military said there was intense fighting in the streets and confirmed that the rebels were in control of parts of the city.
"Our troops are holding their positions, and they are well within their rights to return fire and hold the positions that they have held for several months," Interfax quoted spokesman Andriy Lysenko as saying.
Safe corridor'
A National Guard source in the area told the BBC that government forces had regained control of the supply route, enabling them to get food and medicine into the town and wounded soldiers out.
Meanwhile, Russia's LifeNews website reported that rebel leader Alexander Zakharchenko had been lightly wounded in the leg during the fighting in Debaltseve and had been evacuated from the city.
Rebels have offered Ukrainian troops under siege there a safe corridor to leave.
Although Debaltseve has suffered weeks of artillery exchanges, correspondents say this is the first fierce fighting inside the town.
Most of Debaltseve's 25,000 population have been evacuated but about 7,000 civilians are still believed trapped by the fighting, according to Amnesty International.
The BBC's David Stern in Kiev says there is great concern about the humanitarian situation, with water now running out.